1. Field of the Invention
The present invention relates to a head for a rock drill for an abrasive drilling of stone or stone-like materials and subjected to a rotary-percussion movement, with the head having at least one hard-material insert.
2. Description of the Prior Art
Conventional rock drills usually include a hard-material element in form of a hard-material plate or a head which is formed entirely of a hard material. The hard-material plate is secured in a tool head which adjoins a stem of the tool that is often provided with a helically shaped passage. The stem ends with a shank receivable in a chuck of a drilling tool.
European Publication EP 937 860 A1 discloses a head with a plurality of hard-material inserts located in grooves, which are formed in the head, and forming three plate-shaped bits arranged above a central cylindrical rough-cutting bit.
German Publication DE 197 03 994 A1 discloses a rock drill with a one-piece main bit with two adjacent auxiliary bits which all are formed of three plate-shaped, hard-material inserts and are arranged in a shaped pattern.
German Publication DE 197 09 771 A1 discloses a head, which is formed entirely of a hard material and has two main cutting edges and two auxiliary cutting edges provided on the end surface of the head, with the head including axially engaging elements.
U.S. Pat. No. 5,836,410 discloses a plate-shaped main bit provided, in the region of the drill axis, on its opposite sides with a radial reinforcement forming a rough-cutting edge. The reinforcement has a circular cross-section, in a plane extending perpendicular to the head axis, and is arranged in a coaxial cylindrical recess formed in the head.
U.S. Pat. Nos. 5,220,967 and 4,603,751 disclose a head with a single plate-shaped, main bit arranged in a groove formed in the head. The bit has an axial projection that engages in a coaxial recess formed in the head and provides for radial self-centering of the bit during its securing.
An object of the present invention is a rock drill head with a plurality of hard-material, plate-shaped inserts which self-center upon being secured in the head.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a rock drill head including at least one radially extending groove, a recess formed inside the groove, and at least two, substantially plate-shaped, hard-material inserts located in the groove and having each a radially extending, segment engaging in the circular recess. Upon being secured in the radially extending groove, the hard-material inserts radially self-center, radially inwardly, due to cooperation of respective inner surfaces of the inserts and, radially outwardly, due to formlocking engagement of respective arcuate, e.g., circular or elliptical segments in the recess formed in the head. The projecting radially outwardly, arcuate segments complement the thicknesses of the plate-shaped inserts, forming a circumferentially complete body that formlockingly fills the recess in which they are engaged.
Advantageously, the central cutting tip is formed either as an integral component of one of the inserts or is formed as a separate, compact rough-cutting insert or bit.
It is to be pointed out that providing a head having a plurality of plate-shaped, hard-material inserts instead of a head formed completely of a hard material, provides definite manufacturing advantages consisting in simplified manufacturing of the head and in the possibility of using different inserts.
Further, a greater tolerance is available with respect to the angular arrangement of the cutting edges relative to the radially extending grooves in the head in comparison with the arrangement of single cutting edge-forming legs provided in the hard-material head and inclined because of the distortion due to sintering. The inclination of the cutting edge-forming legs requires that the legs have a sufficient thickness. Thereby, the inserts according to the present invention can have a reduced thickness.
The reduced thickness of the inserts permits to increase the cross-section available for removal of the drilling dust and drillings, which increases the drilling capacity of the drill equipped with a head according to the present invention.
According to a first embodiment of the present invention, two, three or more substantially plate-shaped, hard-material inserts are arranged diametrically or in form of a star about a central cutting tip or rough-cutting edge, with the rough-cutting edge forming an integral component of one of the inserts.
According to another advantageous embodiment of the present invention, one insert forms two, diametrically opposite, main cutting edges on opposite sides of a rough-cutting edge, with the head further including two auxiliary cutting edges forming together with the two main cutting edges a shaped arrangement of the cutting edges.
Advantageously, separate inserts are formed of different hard materials in accordance with a load acting on the separate inserts. E.g., with an shaped arrangement, the main cutting edge-forming insert is formed of a particularly hard material such as ceramics in order to be able to drill a stone material without any noticeable wear, whereas the auxiliary cutting edge-forming insert is formed of a sufficiently hard but not very hard material such as, e.g., hard metal. The auxiliary cutting edge should not break when encountering a reinforcement, and is adjoined by a run-on ramp to provide for lifting of the drill head before the contact of the main cutting edge with the reinforcement.
No additional means are necessary, such as used for retaining dowels, when securing separate hard-material inserts in the radially extending grooves and the recess, as the inserts are formlockingly retained there.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantage and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.